The objectives of the present research projects are to (a) investigate the functional contributions made by the neocortical and thalamic subdivisions of the auditory nervous system to normal binaural hearing, and (b) to attempt to determine the functional significance of bilateral paired structures at the thalamic and cortical levels. Cats will be trained with shock avoidance procedures to respond to various auditory cues presented individually to each ear via earphones. Before and after surgical operations involving combinations of unilateral and bilateral lesions at the level of the neocortex and/or the brachium of the inferior colliculus cats will be tested to determine possible lesion-related changes in both monaural discrimination and binaural integrative capacities. The monaural tests will include determinations of (1) the cat's absolute acuity for detecting tonal signals in the presence or absence of masking noise, (2) the thresholds for detecting changes in the intensity or freqency of on- going auditory signals, and (3) the ability to solve problems involving changes in the duration or patterning of auditory signals. The binaural tests will involve measurements of (1) the masking (and "unmasking" effects of signals at one ear on the detection threshold for signals at the opposite ear, and (2) the thresholds for detecting reversals in the interaural intensity or phase relations of binaurally presented signals. Following the completion of testing, histological verificaton of the locus and extent of the lesions will be determined and this data will be correlated with the observed behavioral changes.